The primary purpose of a network switch is to connect multiple devices on a local area network (LAN). It operates at the data link layer of the OSI model, facilitating the forwarding of data packets based on their MAC addresses. This enhances network efficiency by ensuring that data is sent only to the intended device, reducing unnecessary traffic and collisions. Moreover, switches can manage the flow of data, ensure network segmentation, and provide features like VLANs, which further optimize network performance.